A) nitrogen fixation
B) nitrification
C) operation of biogeochemical cycles
D) All of the above
Correct Answer: D
Solution :
Bacteria is useful in all given activities. The bacteria are important agents in maintaining seed fertility by nitrogen fixation and nitrification. The fixation of nitrogen is brought about asymbiotically by Clostridium (anaerobic), Azotobacter (aerobic), Rhodospirillum, Beijerinkia etc and symbiotically by Rhizobium (in the root nodules of legumes), Actinomycetes etc. The nitrification (conversion of ammonia to nitrates) is brought about by Nitrosomonas and Nitrobacter. The material cycles or biogeochemical cycles in an ecosystem are completed by microbial (bacterial) activities.
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